Association between salivary amylase (AMY1) gene copy numbers and insulin resistance in asymptomatic Korean men

The role of AMY1 gene copy number variation in dental caries susceptibility: insights from a Turkish population

OBJECTIVE

Dental caries is a multifactorial disease influenced by environmental, behavioral, and genetic factors. Recent studies suggest that variations in the AMY1 gene, which encodes salivary amylase, may contribute to caries susceptibility. This study investigates the relationship between AMY1 gene copy number variation (CNV) and dental caries in a Turkish population.

METHOD

A total of 154 participants (63% female; mean age 19.6 ± 1.4 years) were included. Epithelial cells in inner cheek tissues were collected from volunteers using swabs, and the collected samples were preserved and stored in a DNA stabilization solution. The demographic characteristics of the volunteers were recorded, and DMFT and DMFS index scores were documented on the provided forms. The AMY1 gene CNVs were determined using a Real-time polymerase reaction device. The TaqMan chemistry, which comprises quantitative real-time PCR reactions utilizing a dual TaqMan kit, was utilized in this analysis process. Statistical analyses included the Kruskal-Wallis and Mann-Whitney U tests for group comparisons, Spearman's correlation analysis, and binomial logistic regression to evaluate associations between AMY1 CNVs and dental caries indices.

RESULTS

No statistically significant differences were observed between AMY1 CNVs and DMFT or DMFS indices (p > 0.05). However, significant associations were found between daily tooth brushing frequency and caries indices (Cramer's V = 0.219, p < 0.05), as well as between preferred beverage consumption and caries indices (Cramer's V = 0.219, p < 0.05). Other factors, including gender, dental floss and mouthwash use, and tongue brushing, did not show statistically significant associations (p > 0.05).

CONCLUSION

Although AMY1 CNVs were not significantly associated with caries indices, the findings highlight the complex interplay of genetic, behavioral, and dietary factors in caries development. This study emphasizes the critical role of oral hygiene and dietary habits in caries prevention and underscores the need for further research on genetic contributions to oral health.

CLINICAL TRIAL NUMBER

Not applicable.

Salivary α-amylase activity is associated with cardiometabolic and inflammatory biomarkers in overweight/obese, non-diabetic Qatari women

INTRODUCTION

Obesity, prevalent in approximately 80% of Qatar's adult population, increases the risk of complications like type 2 diabetes and cardiovascular diseases. Predictive biomarkers are crucial for preventive strategies. Salivary α-amylase activity (sAAa) inversely correlates with obesity and insulin resistance in adults and children. However, the connection between sAAa and cardiometabolic risk factors or chronic low-grade inflammation markers remains unclear. This study explores the association between serum sAAa and adiposity markers related to cardiovascular diseases, as well as markers indicative of chronic low-grade inflammation.

METHODS

Serum samples and clinical data of 1500 adult, non-diabetic, Overweight/Obese participants were obtained from Qatar Biobank (QBB). We quantified sAAa and C reactive protein (CRP) levels with an autoanalyzer. Cytokines, adipokines, and adiponectin of a subset of 228 samples were quantified using a bead-based multiplex assay. The associations between the sAAa and the adiposity indices and low-grade inflammatory protein CRP and multiple cytokines were assessed using Pearson's correlation and adjusted linear regression.

RESULTS

The mean age of the participants was 36 ± 10 years for both sexes of which 76.6% are women. Our analysis revealed a significant linear association between sAAa and adiposity-associated biomarkers, including body mass index β -0.032 [95% CI -0.049 to -0.05], waist circumference β -0.05 [95% CI -0.09 to -0.02], hip circumference β -0.052 [95% CI -0.087 to -0.017], and HDL β 0.002 [95% CI 0.001 to 0.004], albeit only in women. Additionally, sAAa demonstrated a significant positive association with adiponectin β 0.007 [95% CI 0.001 to 0.01]while concurrently displaying significant negative associations with CRP β -0.02 [95% CI -0.044 to -0.0001], TNF-α β -0.105 [95% CI -0.207 to -0.004], IL-6 β [95% CI -0.39 -0.75 to -0.04], and ghrelin β -5.95 [95% CI -11.71 to -0.20], specifically within the female population.

CONCLUSION

Our findings delineate significant associations between sAAa and markers indicative of cardiovascular disease risk and inflammation among overweight/obese adult Qatari females. Subsequent investigations are warranted to elucidate the nuances of these gender-specific associations comprehensively.

What is the clinical significance of low serum amylase? Systematic review of the conditions associated with low serum amylase

OBJECTIVE

Most studies have assessed the impact of elevated serum amylase levels in clinical practice, but only a few have investigated the significance of low serum amylase. We therefore, aimed to review the literature to understand the conditions associated with low serum amylase and its clinical relevance.

METHOD

This systematic review was performed in accordance with the criteria established in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The search was conducted on Medline and Embase databases until November 2022. After identifying relevant titles, abstracts were read and data of eligible articles retrieved. The conditions associated with low serum amylase were evaluated. The quality of the studies was assessed using the Newcastle-Ottawa Score.

RESULTS

Our search strategy identified 19 studies including a total of 15 097 patients for systematic review. All the studies were observational including two studies which used secretin-induced test. The main conditions associated with low serum amylase were diabetes mellitus (n=9), metabolic syndrome (n=3), chronic pancreatitis (CP) (n=3), non-alcoholic fatty liver disease (n=2) and obesity (n=1). Low serum amylase showed a high specificity (94%) with low sensitivity (38.7%-59%) in diagnosing chronic pancreatitis.

CONCLUSION

This systematic review revealed a unique insight into the relevance of low serum amylase in clinical practice. Low serum amylase can be a useful adjunct test in the assessment of patients with CP, pancreatic exocrine insufficiency, diabetes mellitus and metabolic syndrome.

Gut microbial features and dietary fiber intake predict gut microbiota response to resistant starch supplementation

Resistant starch (RS) consumption can have beneficial effects on metabolic health, but the response, in terms of effects on the gut microbiota and host physiology, varies between individuals. Factors predicting the response to RS are not yet established and would be useful for developing precision nutrition approaches that maximize the benefits of dietary fiber intake. We sought to identify predictors of gut microbiota response to RS supplementation. We enrolled 76 healthy adults into a 7-week crossover study with 59 individuals completing the study. Participants consumed RS type 2 (RS2), RS type 4 (RS4), and digestible starch, for 10 d each with 5-d washout periods in between. We collected fecal and saliva samples and food records during each treatment period. We performed 16S rRNA gene sequencing and measured fecal short-chain fatty acids (SCFAs), salivary amylase (AMY1) gene copy number, and salivary amylase activity (SAA). Dietary fiber intake was predictive of the relative abundance of several amplicon sequence variants (ASVs) at the end of both RS treatments. AMY1-related metrics were not predictive of response to RS. SAA was only predictive of the relative abundance of one ASV after digestible starch supplementation. Interestingly, SCFA concentrations increased the most during digestible starch supplementation. Treatment order (the order of consumption of RS2 and RS4), alpha diversity, and a subset of ASVs were predictive of SCFA changes after RS supplementation. Based on our findings, dietary fiber intake and gut microbiome composition would be informative if assessed prior to recommending RS supplementation because these data can be used to predict changes in specific ASVs and fecal SCFA concentrations. These findings lay a foundation to support the premise that using a precision nutrition approach to optimize the benefits of dietary fibers such as RS could be an effective strategy to compensate for the low consumption of dietary fiber nationwide.

Dental caries prevalence and severity positively associate with AMY1 gene copy number

OBJECTIVE

To establish the possible relation between total caries (TC) and caries severity (CS) with the AMY1 gene copy number (AMY1GCN).

MATERIALS AND METHODS

This was an observational, cross-sectional, population-based, and association study with 303 participants. Each participant underwent a complete anamnesis and stomatological check-up, and peripheral blood was obtained to extract gDNA. TC and CS were determined as the number of caries at the dental exploration and the number of dental surfaces affected by caries, respectively, and AMY1GCN was determined by qPCR.

RESULTS

We found an elevated caries prevalence (92.7%); TC and CS were 8 ± 10 and 10 ± 13 (median ± IR). There were higher TC and CS in those participants with AMY1GCN above the mean value (0.02 and 0.01 p values, respectively). A positive correlation between TC and CS with AMY1GCN (0.11 and 0.125 r values, 0.03 and 0.01 p values, respectively) was found, in addition to an association between TC and CS with AMY1GCN (1.5 and 1.6 OR values, 0.48 and 0.26 p values, respectively).

CONCLUSION

TC and CS were positively related to the AMY1GCN.

CLINICAL RELEVANCE

Dental caries has a high prevalence and a multifactorial etiology and has been related to a genetic component. Indeed, the salivary enzyme alpha-amylase could play a significant role in caries susceptibility, considering that its codifying gene (AMY1) can show variation in its gene copy number. This can be considered an important factor for the development of caries at a genetic level.

Anti-Incretin Gut Features Induced by Feed Supplementation with Alpha-Amylase: Studies on EPI Pigs

The acini-islet-acinar (AIA) axis concept justifies the anatomical placement of the Langerhans islets within the exocrine pancreatic parenchyma and explains the existence of the pancreas as a single organ. Amylase has been suggested to play a key role as an anti-incretin factor. Oral glucose tolerance tests (OGTT) were performed on 18 piglets in both a healthy (prior to pancreatic duct ligation (PDL) surgery, study Day 10) and an exocrine pancreatic insufficient (EPI) state (30 days after PDL, study Day 48)). Amylase (4000 units/feeding) or Creon® (100,000 units/feeding) was administered to pigs with the morning and evening meals, according to study design randomization, for 37 days following the first OGTT. Blood glucose levels, as well as plasma levels of insulin, GLP-1, and GIP, were measured, and the HOMA-IR index was calculated. EPI status did not affect the area under the curve (AUC) of insulin release, fasting insulin levels, or the HOMA-IR index, while amylase supplementation led to a significant (p < 0.05) decrease in the above-mentioned parameters. At the same time, EPI led to a significant (p < 0.05) increase in GLP-1 levels, and neither amylase nor Creon® supplementation had any effects on this EPI-related increase. Fasting plasma levels of GIP were not affected by EPI; however, the GIP response in EPI and Amylase-treated EPI animals was significantly lower (p < 0.05) when compared to that of the intact, healthy pigs. Orally administered amylase induces gut anti-incretin action, normalizing glucose homeostasis and reducing HOMA-IR as a long-term outcome, thus lowering the risk of diabetes type II development. Amylase has long-lasting anti-incretin effects, and one could consider the existence of a long-lasting gut memory for amylase, which decreases hyperinsulinemia and hyperglycemia for up to 16 h after the last exposure of the gut to amylase.

Effect of Aerobic Exercise in Chinese Adult Individuals at Risk for Type 2 Diabetes Mellitus (T2DM) with Low Salivary Amylase Gene (AMY1) Copy Number Variation

Purpose

Type 2 Diabetes mellitus (T2DM) has become a life-threatening health problem around the world. Studies have confirmed that aerobic exercise can prevent the risk of T2DM. Furthermore, recent research showed that salivary amylase gene (AMY1) copy number variation (CNV) could be one of the genetic factors that increased the risk of T2DM. To provide more evidence on how AMY1 CNV and exercise is correlated with the risk of T2DM, we designed this study to show the differences in postprandial carbohydrate metabolism between people with different AMY1 copy numbers, and how aerobic exercise can influence this process.

Participants and Methods

Sixteen participants without cardiovascular disease were chosen, 8 with AMY1 CNV≥6 (High CNV group, HCNV), and 8 with AMY1 CNV ≤ 2 (Low CNV group, LCNV). All participants were Chinese, Han nationality, 18 to 40 years old, with fasting blood glucose lower than 6.1 mmol/L and normal blood pressure levels. They were asked to visit the laboratory in fasting state and drink a cup of solution with 75 grams of edible carbohydrate (glucose or starch). After carbohydrate intake, blood samples were taken at certain times at rest or after aerobic exercise. Blood glucose levels were tested with a portable blood glucose monitor, and insulin levels were tested with the enzyme-linked immunosorbent assay (ELISA).

Results

The LCNV group had significantly higher resting insulin levels and homeostatic model assessment of insulin resistance (HOMA-IR) than the HCNV group. Compared to the HCNV group, postprandial blood glucose levels and insulin levels were insensitive to starch intake in the LCNV group. However, this difference disappeared after aerobic exercise was added as an intervention.

Conclusion

Lower AMY1 CNV could be associated with higher risk of T2DM and complex carbohydrate metabolism disorder, while aerobic exercise can reduce the risk by increasing the carbohydrate utilization rate.

Salivary amylase gene (AMY1) copy number variation has only a minor correlation with body composition in Chinese adults

BACKGROUND

According to the WHO, about 39% of the global adult population were overweight or obese in 2016. Obesity has high heritability, with more than 1000 variants so far identified. There have been reports indicating that salivary amylase gene (AMY1) copy number was one of these variants, yet its association with obesity remains controversial.

OBJECTIVE

Our research aimed to provide more evidence on the relationship of AMY1 copy number variation (CNV) with body mass index (BMI) and body composition.

METHODS

We recruited 133 Chinese adults (65 males, 68 females, 18-25 years old) with normal fasting blood glucose and blood pressure levels. 19 males were selected for a 10-week intervention to change body composition. After anthropometric measurements, BMI was calculated, and body composition was measured using dual energy X-ray absorptiometry (DEXA). For the 19 selected participants, we collected their height, weight, and body composition data one more time after intervention. All participants were required to leave their saliva samples and their AMY1 copy number was determined by real-time fluorescence quantitative PCR.

RESULTS

We failed to find any significant difference in BMI and body composition between different copy number groups. Only a weak correlation was found between body muscle mass and body fat mass. After adjusted for height and weight, AMY1 CNV explained 4.83% of the variance and one single increase in AMY1 CNV can increase 0.214 kg of the body muscle mass, while one single increase in AMY1 CNV can decrease 0.217 kg of the body fat mass and explained 4.69% of the variance.

CONCLUSIONS

As a genetic factor, the AMY1 gene copy number variation has only a minor correlation with BMI and body composition, and its effect can easily be hidden by other factors such as individual diet and exercise habit.

Gut microbial features and dietary fiber intake predict gut microbiota response to resistant starch supplementation

Resistant starch (RS) consumption can have beneficial effects on human health, but the response, in terms of effects on the gut microbiota and host physiology, varies between individuals. Factors predicting the response to RS are not yet established and would be useful for developing precision nutrition approaches that maximize the benefits of dietary fiber intake. We sought to identify predictors of gut microbiota response to RS supplementation. We enrolled 76 healthy adults into a seven-week crossover study. Participants consumed RS type 2 (RS2), RS type 4 (RS4), and a digestible starch, for ten days each with five-day washout periods in between. We collected fecal and saliva samples and food records before and during each treatment period. We performed 16S rRNA gene sequencing and measured fecal short-chain fatty acids (SCFAs), salivary amylase gene copy number, and salivary amylase activity (SAA). Dietary fiber intake was predictive of relative abundance of several amplicon sequence variants (ASVs) at the end of both RS treatments. Treatment order (the order of consumption of RS2 and RS4), alpha diversity, and a subset of ASVs were predictive of SCFA changes after RS supplementation. SAA was only predictive of the relative abundance of ASVs after digestible starch supplementation. Based on our findings, dietary fiber intake and gut microbiome composition would be informative if assessed prior to recommending RS supplementation. Using a precision nutrition approach to optimize the benefits of dietary fibers such as RS could be an effective strategy to compensate for the low consumption of dietary fiber nationwide.

Alterations of the gut microbiota in type 2 diabetics with or without subclinical hypothyroidism

Background

Diabetes and thyroid dysfunction are two closely related endocrine diseases. Increasing evidences show that gut microbiota plays an important role in both glucose metabolism and thyroid homeostasis. Meanwhile, copy number variation (CNV) of host salivary α-amylase gene (AMY1) has been shown to correlate with glucose homeostasis. Hence, we aim to characterize the gut microbiota and CNV of AMY1 in type 2 diabetes (T2D) patients with or without subclinical hypothyroidism (SCH).

Methods

High-throughput sequencing was used to analyze the gut microbiota of euthyroid T2D patients, T2D patients with SCH and healthy controls. Highly sensitive droplet digital PCR was used to measure AMY1 CN.

Results

Our results revealed that T2D patients have lower gut microbial diversity, no matter with or without SCH. The characteristic taxa of T2D patients were Coriobacteriales, Coriobacteriaceae, Peptostreptococcaceae, Pseudomonadaceae, Collinsella, Pseudomonas and Romboutsia. Meanwhile, Escherichia/Shigella, Lactobacillus_Oris, Parabacteroides Distasonis_ATCC_8503, Acetanaerobacterium, Lactonifactor, uncultured bacterium of Acetanaerobacterium were enriched in T2D patients with SCH. Moreover, serum levels of free triiodothyronine (FT3) and free thyroxine (FT4) in T2D patients were both negatively correlated with richness of gut microbiota. A number of specific taxa were also associated with clinical parameters at the phylum and genus level. In contrast, no correlation was found between AMY1 CN and T2D or T2D_SCH.

Conclusion

This study identified characteristic bacterial taxa in gut microbiota of T2D patients with or without SCH, as well as the taxa associated with clinical indices in T2D patients. These results might be exploited in the prevention, diagnosis and treatment of endocrine disorders in the future.

The roles of personalized nutrition in obesity and diabetes management: a review

Background & Aims

Nutrition is one of main environmental factor affecting obesity and its related complications such as diabetes and dyslipidemia. Due to growing prevalence of obesity across the world, it seems that nutritional advice alone is not able to combat this health problem. The present overview aimed to summarize the roles of personalized nutrition (PN) in obesity and diabetes management.

Methods

Scopus, PubMed and Google scholar were searched up to February 2021 to find relevant studies with English language in which the roles of PN in obesity and diabetes management were examined.

Results

Recent evidence revealed the importance of gene-environment interactions for management of diabetes mellitus and obesity. Moreover, microbiome research showed that personalized diet based on a combination of clinical and microbial features is likely to improve responses to therapeutic interventions. Epigenetics as well as genetic and environmental factors can also contribute to the treatment. In addition, articles showed significant roles of epigenetics and gut microbiome on providing an individualized diet for obese and diabetic patients.

Conclusion

PN compare to conventional diet can better improve metabolic status in obese and diabetic patients. Considering genetic differences and microbiome patterns along with environmental factors and their interactions are recommended for obesity and diabetes management. This approach can increase success in promoting health and preventing complications related to diabetes and obesity.

Elevated levels of salivary α- amylase activity in saliva associated with reduced odds of obesity in adult Qatari citizens: A cross-sectional study

The relationship between salivary α-amylase activity (ssAAa) and the risk of metabolic disorders remains equivocal. We aimed to assess this relationship in adults from Qatar, where obesity and type 2 diabetes are highly prevalent. We cross-sectionally quantified ssAAa in saliva and estimated AMY1 CN from whole-genome sequencing data from 1499 participants. Linear regression was used to assess the relationship between ssAAa and adiposity and glycemic markers. Logistic regression was used to examine the association between ssAAa and occurrence of obesity or diabetes. The mean and median ssAAa were significantly lower in obese individuals. There were significant inverse associations between ssAAa and BMI, and fat mass. We detected a marked effect of ssAAa on reduced odds of obesity after adjusting for age and sex, glucose, LDL, HLD, total cholesterol, and systolic and diastolic blood pressure (OR per ssAAa unit 0.998 [95% CI 0.996-0.999], p = 0.005), with ssAAa ranging between 6.8 and 422U/mL. The obesity odds were significantly lower in the upper half of the ssAAa distributional (OR 0.58 [95% CI 0.42-0.76], p<0.001) and lower in the top versus the bottom decile of the ssAAa distribution (OR 0.46 [95% CI 0.23-0.92], p = 0.03). Our findings suggest a potential beneficial relationship between high sAAa in saliva and low odds of obesity in Qatari adults.

Sea Buckthorn (Hippophae rhamnoides) Waste Biomass after Harvesting as a Source of Valuable Biologically Active Compounds with Nutraceutical and Antibacterial Potential

For sustainable sea buckthorn (Hippophae rhamnoides) berry production, the task at hand is to find an application for the large amount of biomass waste arising at harvesting. Sea buckthorn (SBT) vegetation is currently poorly studied. The purpose of this research was to assess the composition and potential of SBT twigs as a source of valuable biologically active substances. Water and 50% EtOH extracts of twigs of three Latvian SBT cultivars with a high berry yield and quality, popular for cultivation in many countries (H. rhamnoides 'Maria Bruvele', 'Tatiana', 'Botanicheskaya Lubitelskaya'), were investigated for the first time. The phytochemical composition (UHPLC-ESI-MS/MS analysis) and biological activity of the obtained hydrophilic extracts were determined. The highest yield of polyphenolic compounds and serotonin was observed for 'Maria Bruvele'. Hydrophilic extracts were investigated for radical scavenging activity (DPPH˙ test), antibacterial/antifungal activity against five pathogenic bacteria/yeast, cytotoxicity, and the enzymatic activity of alpha-amylase (via in vitro testing), which is extremely important for the treatment of people with underweight, wasting, and malabsorption. The results showed a high potential of sea buckthorn biomass as a source of valuable biologically active compounds for the creation of preparations for the food industry, nutraceuticals, and cosmetics.

Enzyme kinetic approach for mechanistic insight and predictions of in vivo starch digestibility and the glycaemic index of foods

BACKGROUND

Starch is a principal dietary source of digestible carbohydrate and energy. Glycaemic and insulinaemic responses to foods containing starch vary considerably and glucose responses to starchy foods are often described by the glycaemic index (GI) and/or glycaemic load (GL). Low GI/GL foods are beneficial in the management of cardiometabolic disorders (e.g., type 2 diabetes, cardiovascular disease). Differences in rates and extents of digestion of starch-containing foods will affect postprandial glycaemia.

SCOPE AND APPROACH

Amylolysis kinetics are influenced by structural properties of the food matrix and of starch itself. Native (raw) semi-crystalline starch is digested slowly but hydrothermal processing (cooking) gelatinises the starch and greatly increases its digestibility. In plants, starch granules are contained within cells and intact cell walls can limit accessibility of water and digestive enzymes hindering gelatinisation and digestibility. In vitro studies of starch digestion by α-amylase model early stages in digestion and can suggest likely rates of digestion in vivo and expected glycaemic responses. Reports that metabolic responses to dietary starch are influenced by α-amylase gene copy number, heightens interest in amylolysis.

KEY FINDINGS AND CONCLUSIONS

This review shows how enzyme kinetic strategies can provide explanations for differences in digestion rate of different starchy foods. Michaelis-Menten and Log of Slope analyses provide kinetic parameters (e.g., K m and k cat /K m ) for evaluating catalytic efficiency and ease of digestibility of starch by α-amylase. Suitable kinetic methods maximise the information that can be obtained from in vitro work for predictions of starch digestion and glycaemic responses in vivo.

Effect of AMY1 copy number variation and various doses of starch intake on glucose homeostasis: data from a cross-sectional observational study and a crossover meal study

Background

Copy number (CN) variation (CNV) of the salivary amylase gene (AMY1) influences the ability to digest starch and may influence glucose homeostasis, obesity and gut microbiota composition. Hence, the aim was to examine the association of AMY1 CNV with fasting glucose, BMI, and gut microbiota composition considering habitual starch intake and to investigate the effect of AMY1 CNV on the postprandial response after two different starch doses.

Methods

The Malmö Offspring Study (n = 1764, 18–71 years) was used to assess interaction effects between AMY1 CNV (genotyped by digital droplet polymerase chain reaction) and starch intake (assessed by 4-day food records) on fasting glucose, BMI, and 64 gut bacteria (16S rRNA sequencing). Participants with low (≤ 4 copies, n = 9) and high (≥ 10 copies, n = 10) AMY1 CN were recruited for a crossover meal study to compare postprandial glycemic and insulinemic responses to 40 g and 80 g starch from white wheat bread.

Results

In the observational study, no overall associations were found between AMY1 CNV and fasting glucose, BMI, or gut microbiota composition. However, interaction effects between AMY1 CNV and habitual starch intake on fasting glucose (P = 0.03) and BMI (P = 0.05) were observed, suggesting inverse associations between AMY1 CNV and fasting glucose and BMI at high starch intake levels and positive association at low starch intake levels. No associations with the gut microbiota were observed. In the meal study, increased postprandial glucose (P = 0.02) and insulin (P = 0.05) were observed in those with high AMY1 CN after consuming 40 g starch. This difference was smaller and nonsignificant after consuming 80 g starch.

Conclusions

Starch intake modified the observed association between AMY1 CNV and fasting glucose and BMI. Furthermore, depending on the starch dose, a higher postprandial glucose and insulin response was observed in individuals with high AMY1 CN than in those with low AMY1 CN.

Trial registration

ClinicalTrials.gov, NCT03974126. Registered 4 June 2019—retrospectively registered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12263-021-00701-8.

Dietary carbohydrates interact with AMY1 polymorphisms to influence the incidence of type 2 diabetes in Korean adults

The relationship between AMY1 single nucleotide polymorphisms (SNPs), dietary carbohydrates, and the risk of type 2 diabetes is unclear. We aimed to evaluate this association using an ongoing large-scale prospective study, namely the Korean Genome and Epidemiology Study. We selected six genetic variants of the AMY1 gene: rs10881197, rs4244372, rs6696797, rs1566154, rs1930212, and rs1999478. Baseline dietary data were obtained using a semi-quantitative food frequency questionnaire. Type 2 diabetes was defined according to the criteria of the World Health Organization and American Diabetes Association. During an average follow-up period of 12 years (651,780 person-years), 1082 out of 4552 (23.8%) patients had type 2 diabetes. Three AMY1 SNPs were significantly associated with diabetes incidence among patients with carbohydrate intake > 65% of total energy: rs6696797, rs4244372, and rs10881197. In multivariable Cox models, Korean women with the rs6696797 AG or AA genotype had 28% higher incidence of type 2 diabetes (hazard ratio 1.28, 95% confidence interval 1.06-1.55) than Korean women with the rs6696797 GG genotype. We did not observe significant associations between AMY1 SNPs, dietary carbohydrates, and diabetes incidence in Korean men. We conclude that AMY1 genetic variants and dietary carbohydrate intake influence the incidence of type 2 diabetes in Korean women only. Korean women who are minor carriers of the AMY1 rs6696797, rs4244372, and rs10881197 genotypes may benefit from a low-carbohydrate diet to prevent the future risk of type 2 diabetes.

Reduced odds of diabetes associated with high plasma salivary α-amylase activity in Qatari women: a cross-sectional study

The association of salivary α-amylase activity (SAA) activity or low copy number of its coding gene AMY1 with diabetes remains controversial. We aimed to reinvestigate the association of these factors with diabetes in Qatar, where diabetes prevalence is about 16%. We obtained cross-sectional data of 929 Qataris (age > 18 years) from the Qatar Biobank. We estimated AMY1 copy number variants (CNV) from whole-genome data, and quantified the SAA activity in plasma (pSAA). We used adjusted logistic regression to examine the association between pSAA activity or AMY1 CNV and diabetes odds. We found a significant association between high pSAA activity, but not AMY1 CNV, and reduced odds of diabetes in Qatari women. The OR per pSAA activity unit was 0.95 [95% CI 0.92, 0.98] (p = 0.002) (pSAA activity range: 4.7 U/L to 65 U/L) in women. The association is driven largely by the highest levels of pSAA activity. The probability of having diabetes was significantly lower in the fifth pSAA activity quintile relative to the first (0.21 ± 0.03 (Q1) versus 0.82 ± 0.02 (Q5)), resulting in significantly reduced diabetes prevalence in Q5 in women. Our study indicates a beneficial effect of high pSAA activity, but not AMY1 CN, on diabetes odds in Qatari women, and suggests pSAA activity levels as a potential marker to predict future diabetes in Qatari women.

Influence of AMY1A copy number variations on obesity and other cardiometabolic risk factors: A review of the evidence

The rising incidence of obesity and type 2 diabetes is contributing to the escalating burden of disease globally. These metabolic disorders are closely linked with diet and in particular with carbohydrate consumption; hence, it is important to understand the underlying mechanisms that influence carbohydrate metabolism. Amylase, the enzyme responsible for the digestion of starch, is coded by the genes AMY1A, AMY1B, and AMY1C (salivary amylase) and AMY2A and AMY2B (pancreatic amylase). Previous studies demonstrate wide variations in AMY1A copy numbers, which can be attributed to several genetic, nutritional, and geographical diversities seen in populations globally. Current literature suggests that AMY1A copy number variations are important in obesity and other cardiometabolic disorders through their effects on glucose and lipid homeostasis, inflammatory markers, and the gut microbiome. This review synthesizes the available evidence to improve understanding of the role of AMY1A in obesity and related cardiometabolic risk factors and disorders including insulin resistance and type 2 diabetes, cardiovascular risk and inflammation, and the gut microbiome.

Polymorphisms of AMY1A gene and their association with growth, carcass traits and feed intake efficiency in chickens

Investigations on the association between chicken traits and genetic variations can provide basic information to improve production performance in chickens. In our previous work, we genotyped 450 male chickens with a 600 K SNP array [1] and found that several SNPs in the genomic regions of the amylase alpha 1A (AMY1A) gene were significantly associated with feed intake efficiency and carcass traits. Given the lower accuracy of the SNP array, we performed direct sequencing with male and female chickens to further test chicken AMY1A polymorphisms and investigate their association with 17 traits in chickens. The results showed that 7 SNPs in the 5' flanking region, exon, intron and 3' UTR (3' untranslated region) of AMY1A, were significantly associated with daily gain (DG), average daily feed intake (ADFI), leg muscle weight (LMW) and abdominal fat (AF) (p < 0.05). Additionally, the haplotypes based on three SNPs, rs15910189, rs314354067 and rs316026696, showed significant associations with DG (p < 0.01), ADFI and AF (p < 0.05). To better understand the transcriptional regulation of AMY1A, we cloned its 5' flanking region and found that the SNPs rs316436216 and rs314213090 which might change the transcriptional regulator binding sites, were in the suppressor and enhancer regions, respectively. In addition, luciferase assays revealed that the SNP rs314613110 in the 3' UTR influenced the binding of the miRNA gga-miR-1764-3p. To validate whether there is any copy number variation in AMY1A in our population, we performed a genome-wide assessment of CNVs through whole-genome resequencing data. However, no CNV was found in AMY1A in our population, which is different from the increased copy number of AMY1A found in humans who consume a high-starch diet. Therefore, the present study provides substantial evidence for the association of AMY1A polymorphisms with growth traits and feed intake efficiency, which might contribute to chicken breeding programs.

Interaction Effect Between Copy Number Variation in Salivary Amylase Locus (AMY1) and Starch Intake on Glucose Homeostasis in the Malmö Diet and Cancer Cohort

Salivary amylase initiates the digestion of starch and it has been hypothesized that salivary amylase may play a role in the development of insulin resistance and type 2 diabetes. The aim was to examine the interaction between copy number variation in the salivary amylase gene AMY1 and starch intake. We studied 3,624 adults without diabetes or elevated blood glucose in the Malmö Diet Cancer cohort. We assessed the associations and interactions between starch intake, AMY1 copies and glucose homeostasis traits (i.e., fasting plasma glucose, insulin and HOMA-IR) and risk of type 2 diabetes over an average of 18 follow-up years. AMY1 copy number was not associated with glucose, insulin or HOMA-IR. We observed a significant interaction between starch intake and AMY1 copies on insulin and HOMA-IR after adjusting for potential confounders (p < 0.05). The inverse association between starch intake and insulin and HOMA-IR was stronger in the group with 10 or more copies (P _trend < 0.001). In addition, we observed an inverse association between starch intake and type 2 diabetes in the group with 10 or more copies (p _trend = 0.003), but not in the other groups. This cross-sectional observational study suggests that AMY1 copy numbers might interact with starch intake on glucose homeostasis traits. Interventional studies are required to determine whether individuals with high AMY1 copy numbers may benefit from a high starch intake.

Association of Serum Amylase Activity and the Copy Number Variation of AMY1/2A/2B with Metabolic Syndrome in Chinese Adults

PURPOSE

Low serum amylase activity and copy number (CN) variation (CNV) of the salivary amylase gene (AMY1) are reportedly associated with obesity and abnormal glucose metabolism; however, this association remains controversial. We aimed to clarify the relationship between serum amylase activity and the CNV of AMY1/2A/2B with the occurrence of metabolic syndrome (MetS) in Chinese adults.

PATIENTS AND METHODS

Anthropometry, metabolic risk factors, and serum amylase activity were assessed in 560 subjects (260 MetS patients; 300 healthy controls). AMY1/2A/2B CNs were evaluated using the highly sensitive droplet digital PCR.

RESULTS

The serum total, pancreatic, and salivary amylase activity, but not the AMY1/2A/2B CNs, was significantly lower in MetS patients than that in the control subjects. Patients <45 y had a lower AMY1 CN, compared to that in healthy controls. Low serum amylase activity was significantly associated with high MetS prevalence (p < 0.001). In the receiver operating characteristic curve analysis, serum amylase activity was a significant diagnostic indicator for MetS. The diagnostic value of total amylase was second only to that of γ-glutamyl transpeptidase; it was higher than that of alanine aminotransferase and uric acid.

CONCLUSION

Low serum amylase activity was significantly associated with increased risk of MetS in Chinese adults. Therefore, amylase could be a potential biomarker for predicting MetS.

Alpha-amylase 1A copy number variants and the association with memory performance and Alzheimer's dementia

Background

Previous studies have shown that copy number variation (CNV) in the alpha (α)-amylase gene (AMY1A) is associated with body mass index, insulin resistance, and blood glucose levels, factors also shown to increase the risk of Alzheimer’s dementia (AD). We have previously demonstrated the presence of α-amylase in healthy neuronal dendritic spines and a reduction of the same in AD patients. In the current study, we investigate the relationship between AMY1A copy number and AD, memory performance, and brain α-amylase activity.

Methods and materials

The association between AMY1A copy number and development of AD was analyzed in 5422 individuals (mean age at baseline 57.5 ± 5.9, females 58.2%) from the Malmö diet and cancer study genotyped for AMY1A copy number, whereof 247 where diagnosed with AD during a mean follow-up of 20 years. Associations between AMY1A copy number and cognitive performance where analyzed in 791 individuals (mean age at baseline 54.7 ± 6.3, females 63%), who performed Montreal Cognitive Assessment (MoCA) test. Correlation analysis between α-amylase activity or α-amylase gene expression and AMY1A copy number in post-mortem hippocampal tissue from on demented controls (n = 8) and AD patients (n = 10) was also performed.

Results

Individuals with very high ( ≥10) AMY1A copy number had a significantly lower hazard ratio of AD (HR = 0.62, 95% CI 0.41–0.94) and performed significantly better on MoCA delayed word recall test, compared to the reference group with AMY1A copy number 6. A trend to lower hazard ratio of AD was also found among individuals with low AMY1A copy number (1–5) (HR = 0.74, 95% CI 0.53–1.02). A tendency towards a positive correlation between brain α-amylase activity and AMY1A copy number was found, and females showed higher brain α-amylase activity compared to males.

Conclusion

Our study suggests that the degree of α-amylase activity in the brain is affected by AMY1A copy number and gender, in addition to AD pathology. The study further suggests that very high AMY1A copy number is associated with a decreased hazard ratio of AD and we speculate that this effect is mediated via a beneficial impact of AMY1A copy number on episodic memory performance.

High plasma salivary α-amylase, but not high AMY1 copy number, associated with low obesity rate in Qatari adults: cross-sectional study

The relationship between salivary α-amylase activity (psAAa) or AMY1 copy number and the risk of obesity remains controversial. We aimed to assess this relationship in a cohort from Qatar, where obesity affects 43% of adults. The relationship was investigated cross-sectionally in 923 Qatari adults from the Qatar biobank cohort. AMY1 CN was estimated form whole genome sequencing data. The associations with obesity prevalence were assessed by linear and logistic regressions. We found no difference in AMY1 CN between obese and normal-weight individuals. However, the psAAa was significantly lower in obese individuals. Significant inverse correlations were found between adiposity markers and psAAa in both sexes, but were marginally stronger in men. A significant effect of high psAAa, but not AMY1 CN, on reduced obesity rates was identified in men (OR per psAAa unit 0.957 [95% CI 0.937-0.977], p < 0.001, with psAAa ranging between 5 to 66 U/L). A significantly higher prevalence of obesity was observed in the lowest quartile of psAAa in men (75% (Q1) vs. 36% (Q4), p < 0.001) and women (74% (Q1) vs 56% (Q4), p = 0.009). Our findings suggest that high psAAa, but not AMY1 CN, has a potential positive benefit against obesity in the Qatari population.

AMY1 Gene Copy Number Correlates With Glucose Absorption and Visceral Fat Volume, but Not with Insulin Resistance

BACKGROUND

The human amylase gene (AMY1) has a broad copy number (CN) variation that may associate with body mass index.

METHODS

Deoxyribonucleic acid was extracted from urine (n = 74) and serum (n = 6) samples (Protein, Fiber and Metabolic Syndrome [ProFiMet] cohort), and buccal (n = 17) samples (Oral Starch Challenge [OSC] cohort), and assessed for AMY1 CN by droplet digital polymerase chain reaction. The association of AMY1 CN with comprehensive markers of metabolic status (ProFiMet cohort) were analyzed with Pearson's correlation coefficient (CC). For the healthy, euglycemic OSC cohort, glycemic response to OSC was analyzed with independent sample t-tests (subgroups: high AMY1 CN 9-12, n = 10; low AMY1 CN 4-6, n = 7).

RESULTS

There were significant inverse correlations of AMY1 CN with total visceral fat volume (CC -0.33; P = 0.004) and positive correlations of AMY1 CN with oral glucose insulin sensitivity score (derived from an oral glucose tolerance test, CC 0.26; P = 0.02), serum HDL-cholesterol (CC 0.325; P = 0.003), and serum adiponectin (CC 0.249; P = 0.026). Linear regression multivariate analysis (adiponectin as dependent variable), showed independent association of adiponectin with AMY1 CN (Beta = 0.29; P = 0.03). There were no significant associations between AMY1 CN and clamp-derived M-value, homeostasis model assessment of insulin resistance (IR), hepatic endogenous glucose production, fecal floral signature, or macronutrient dietary preference. Delta (mean) change in blood glucose concentration (fasting to 30-minutes post-OSC) was significantly greater in the high versus low AMY1 CN subgroups (mean 1.7 mmol/l [SEM 0.6] vs 0.9 mmol/l [SEM 0.9], respectively; P = 0.016).

CONCLUSIONS

High AMY1 CN associates with a favorable metabolic profile (lower visceral fat volume, higher serum adiponectin, enhanced glucose absorption following oral glucose, and OSC), but not with whole-body or hepatic IR.

AMY1 diploid copy number among end-stage renal disease patients

PURPOSE

The salivary amylase gene (AMY1) copy number variation (CNV) is increased as a human adaptation to starch-enriched nutritional patterns. The purpose of this study was to evaluate the relationship between AMY1 CNV, dietary starch consumption, and anthropometric indices among a known population with elevated cardiovascular risk, being end-stage renal disease (ESRD) patients.

METHODS

A total of 43 ESRD patients were recruited based on the following inclusion criteria: being (1) adults, (2) on hemodialysis for more than 3 months, (3) able to communicate effectively, and (4) willing to participate. Anthropometric measurements were performed, dietary intake was recorded via food-frequency questionnaires, and AMY1 CNV was quantified in blood samples DNA via real-time PCR.

RESULTS

Median AMY1 CNV was 4.0 (2.0-17.0). A total of 21 patients had an even, and 22 had an odd AMY1 copy number (CN). Independent samples t tests revealed that AMY1-odd diploid CN is associated with increased body weight, waist and hip circumferences, and fat mass compared to the respective even diploid CN carrier group. No differences were observed for BMI or nutritional intake. Multiple regression analysis revealed that AMY1-odd diploid CN was positively associated with increased hip circumference (ß = 7.87, 95% CI = 0.34 to 15.39) and absolute fat mass (ß = 6.66, 95% CI = 0.98 to 12.34); however, after applying the Bonferroni correction for multiplicity, all regression analyses lost their significance.

CONCLUSIONS

AMY1-odd diploid CN appears to be associated with selected adiposity variables among hemodialysis patients. However, more research is needed to verify this finding in this population with known increased cardiovascular risk.

Starch Digestion-Related Amylase Genetic Variants, Diet, and Changes in Adiposity: Analyses in Prospective Cohort Studies and a Randomized Dietary Intervention

Salivary amylase, encoded by the AMY1 gene, is responsible for the digestion of carbohydrates. We investigated associations of AMY1 genetic variations with general and central adiposity changes considering dietary carbohydrate intake among 32,054 adults from four prospective cohort studies. A genetic risk score (GRS) was calculated based on nine AMY1 single-nucleotide polymorphisms, with higher AMY1-GRS indicating higher activity of salivary amylase. We meta-analyzed interactions between AMY1-GRS and dietary intake for changes in general and central adiposity over 5.5-10 years. We found that carbohydrate food intake significantly altered associations of AMY1-GRS with changes in BMI (P interaction = 0.001) and waist circumference (P interaction < 0.001). Results were consistent and significant in female cohorts rather than in male cohorts. Among women, higher AMY1-GRS was associated with more increases in adiposity if dietary carbohydrate food intake was high, while higher AMY1-GRS was associated with less gains in adiposity when the dietary intake was low. Also, in a 2-year randomized dietary intervention trial, associations of AMY1-GRS with changes in weight (P interaction = 0.023) and waist circumference (P interaction = 0.037) were significantly modified by carbohydrate intake. Our results suggest the importance of precision nutrition strategies considering participants' genetic adaptation to carbohydrate-rich diets in regulating general and central adiposity.

Low AMY1 Copy Number Is Cross-Sectionally Associated to an Inflammation-Related Lipidomics Signature in Overweight and Obese Individuals

SCOPE

Reduced amylase 1 (AMY1) copy numbers are associated with obesity, insulin resistance, and inflammation. Although mechanisms linking AMY1 copy number with metabolic disorders are poorly understood, recent findings suggest that lipids play a key role.

METHODS AND RESULTS

Plasma lipidomic signatures associated with AMY1 copy number are explored in 57 non-diabetic overweight/obese subjects aged 18-60. Serum amylase and inflammatory cytokines levels are also measured. AMY1 copy number is strongly associated with the serum amylase concentration. Participants are divided into low-(≤4) and high-(>4) AMY1 carriers based on the median. Low-AMY1 carriers have higher BMI and fat mass. They also have higher levels of dihexosylceramides (R = -0.27, p = 0.044), cholesterol esters (CE) (R = -0.32, p = 0.020), alkylphosphatidylcholines [PC(O)] (R = -0.33, p = 0.014), and sphingomyelins (SM) (R = -0.38, p = 0.005). From 459 lipid species, 28 differ between low- and high-AMY1 carriers. These include CE species with long-chain PUFA; PC(O) and PC plasmalogens containing arachidonic acid; and PC, mono-, di-, and tri-hexosylceramides, and SM containing saturated fatty acids (mainly C16:0 and C20:0). This lipidomic signature is strongly associated with inflammatory cytokines, which are also negatively associated with the AMY1 copy number.

CONCLUSION

A lipidomics signature associated with low AMY1 copy numbers is revealed, which is linked to obesity and chronic low-grade inflammation.

Copy Number Variation of the Salivary Amylase Gene and Glucose Metabolism in Healthy Young Japanese Women

BACKGROUND

Many studies have shown that low copy number variation (CNV) of the salivary amylase gene (AMY1) and low serum amylase concentration are associated with impaired glucose metabolism and obesity. We aimed to clarify the conflicting results of previous studies by examining AMY1 expression and metabolic indices in a homogenous group of healthy participants.

METHODS

Sixty healthy non-obese young Japanese women aged 20 - 39 years were examined for AMY1 CNV, salivary amylase, body mass index (BMI) and serum parameters including glycated hemoglobin (HbA1c), ketones, and total, salivary and pancreatic amylase. Respiratory quotient at rest and changes in blood glucose after starch loading were also examined.

RESULTS

AMY1 CNV (range, 4 - 14) and the level of serum salivary amylase were correlated inversely with HbA1c (r = -0.36, P = 0.003 and r = -0.30, P = 0.02, respectively), whereas the percentage of serum salivary amylase in total serum amylase was positively correlated with blood glucose at 30 and 45 min after starch loading (r = 0.38, P = 0.004 and r = 0.27, P = 0.04, respectively). The level of serum total amylase, but not AMY1 CNV, was correlated inversely with BMI (r = -0.29, P = 0.02). Logistic regression analysis showed that low AMY1 CNV (4 - 7) was significantly associated with an HbA1c of ≥ 5.4% (34 mmol/mol) even after adjustment for age, BMI and energy consumption, compared with high AMY1 CNV (8 - 14).

CONCLUSIONS

Although a higher percentage of serum salivary amylase was associated with higher levels of blood glucose at the early stage after starch loading, low AMY1 CNV was associated with chronic unfavorable glucose metabolism in healthy non-obese young women in Japan.

Genetic Differences in Taste Receptors: Implications for the Food Industry

Inborn genetic differences in chemosensory receptors can lead to differences in perception and preference for foods and beverages. These differences can drive market segmentation for food products as well as contribute to nutritional status. This knowledge may be essential in the development of foods and beverages because the sensory profiles may not be experienced in the same way across individuals. Rather, distinct consumer groups may exist with different underlying genetic variations. Identifying genetic factors associated with individual variability can help better meet consumer needs through an enhanced understanding of perception and preferences. This review provides an overview of taste and chemesthetic sensations and their receptors, highlighting recent advances linking genetic variations in chemosensory genes to perception, food preference and intake, and health. With growing interest in personalized foods, this information is useful for both food product developers and nutrition health professionals alike.

Salivary Amylase Gene Copy Number Is Associated with the Obesity and Inflammatory Markers in Children

BACKGROUND

We have recently shown that the copy number of salivary amylase (AMY1) gene was significantly decreased, and the obesity-related salivary biomarkers resistin, MCP-1, TNF-α, IL-6, and CRP were significantly increased in overweight/obese children compared to normal weight. This study aimed to evaluate the association of AMY1 copy number variant (CNV) with obesity and inflammatory markers. Seventy-six participants aged between 6 and 10 years have participated, and the saliva samples were collected along with the anthropometric measurements.

METHODS

AMY1 copy number was analyzed by 3D digital PCR, and obesity-related biomarkers were performed with a Bioplex multiplex analyzer.

RESULTS

The mean AMY1 copy number was higher in normal weight (7.90 ± 0.38) compared to the overweight/obese group (6.20 ± 0.29). The association of AMY1 CNV with obesity and inflammatory markers showed significant negative correlation [CRP, β = -0.238 (p < 0.05); resistin, β = -0.25 (p < 0.05); MCP-1, β = -0.304 (p < 0.01)] except for complement factor D, TNF α and IL-6. The anti-inflammatory cytokine, IL-10 reported a positive correlation with AMY1 copy number with a β = 0.268 (p < 0.05). The multivariable model adjusted with age and gender depicted a similar correlation with obesity markers.

CONCLUSION

Our results report that AMY1 CNV is associated with obesity and inflammatory biomarkers in children's saliva sample.

Salivary α-amylase copy number is not associated with weight trajectories and glycemic improvements following clinical weight loss: results from a 2-phase dietary intervention study

BACKGROUND

Several studies recently reported contradicting results regarding the link between amylase 1 (AMY1) copy numbers (CNs), obesity, and type 2 diabetes.

OBJECTIVE

The aim of this study was to assess the impact of AMY1 CN on anthropometrics and glycemic outcomes in obese individuals following a 2-phase dietary weight loss intervention.

METHODS

Using the paralog ratio test, AMY1 CNs were accurately measured in 761 obese individuals from the DiOGenes study. Subjects first underwent an 8-wk low-calorie diet (LCD, at 800 kcal/d) and then were randomly assigned to a 6-mo weight maintenance dietary (WMD) intervention with arms having different glycemic loads.

RESULTS

At baseline, a modest association between AMY1 CN and BMI (P = 0.04) was observed. AMY1 CN was not associated with baseline glycemic variables. In addition, AMY1 CN was not associated with anthropometric or glycemic outcomes following either LCD or WMD. Interaction analyses between AMY1 CN and nutrient intake did not reveal any significant association with clinical parameters (at baseline and following LCD or WMD) or when testing gene × WMD interactions during the WMD phase.

CONCLUSION

In the absence of association with weight trajectories or glycemic improvements, the AMY1 CN cannot be considered as an important biomarker for response to a clinical weight loss and weight maintenance programs in overweight/obese subjects. This trial was registered at www.clinicaltrials.gov as NCT00390637.

Increased Inflammation and Cardiometabolic Risk in Individuals with Low AMY1 Copy Numbers

Lower copy number variations (CNVs) in the salivary amylase gene (AMY1) have been associated with obesity and insulin resistance; however, the relationship between AMY1 and cardiometabolic risk has not been fully elucidated. Using gold-standard measures, we aimed to examine whether AMY1 CNVs are associated with cardiometabolic risk factors in an overweight or obese, otherwise healthy population. Fifty-seven adults (58% male) aged 31.17 ± 8.44 years with a body mass index (BMI) ≥25 kg/m² were included in the study. We measured AMY1 CNVs (qPCR); anthropometry (BMI; body composition by dual-energy X-ray absorptiometry); cardiovascular parameters (blood pressure, serum lipids by ELISA); insulin sensitivity (hyperinsulinaemic–euglycaemic clamp), insulin secretion (intravenous glucose tolerance test), and serum inflammation markers (multiplex assays). Based on previous studies and median values, participants were divided into low (≤4) and high (>4) AMY1 CNV groups. Low AMY1 carriers (n = 29) had a higher fat mass (40.76 ± 12.11 versus 33.33 ± 8.50 kg, p = 0.009) and LDL-cholesterol (3.27 ± 0.80 versus 2.87 ± 0.69 mmol/L, p = 0.038), and higher serum levels of interleukin [IL]-6, IL-1β, tumour necrosis factor-alpha and monocyte chemoattractant protein-1 (MCP-1) (all p < 0.05) compared with high AMY1 carriers (n = 28), but there were no differences in glycaemic measures, including insulin sensitivity or secretion (all p > 0.1). Except for MCP-1, the results remained significant in multivariable models adjusted for age, sex, and fat mass (all p < 0.05). Our findings suggest that low AMY1 CNVs are associated with increased cardiovascular disease risk and inflammation, but not glucose metabolism, in overweight or obese adults.

The physiologic and phenotypic significance of variation in human amylase gene copy number

Background

Salivary α-amylase gene (AMY1) copy number (CN) correlates with the amount of salivary α-amylase, but beyond this, the physiologic significance is uncertain.

Objective

We hypothesized that individuals with higher AMY1 CN would digest starchy foods faster and show higher postprandial responses and lower breath hydrogen excretion compared with those with low CN.

Design

Four linked studies were conducted. In Study 1, we genotyped 201 healthy subjects with the use of real-time quantitative polymerase chain reaction and determined glucose tolerance, insulin sensitivity, salivary α-amylase activity, body mass index (BMI), and macronutrient intake. In Study 2, a pool of 114 subjects tested 6 starchy foods, 3 sugary foods, 1 mixed meal, and 2 reference glucose solutions, containing either 50 or 25 g of available carbohydrate. In Study 3, we compared glycemic and insulin responses to starchy foods with responses to glucose in 40 individuals at extremes of high and low CN. In Study 4, we compared breath hydrogen and methane responses over 8 h in 30 individuals at extremes of CN.

Results

AMY1 CN correlated positively with salivary α-amylase activity (r = 0.62, P < 0.0001, n = 201) but not with BMI, glucose tolerance, or insulin sensitivity. However, CN was strongly correlated with normalized glycemic responses to all starchy foods (explaining 26-61% of interindividual variation), but not to sucrose or fruit. Individuals in the highest compared with the lowest decile of CN produced modestly higher glycemia (+15%, P = 0.018), but not insulinemia, after consuming 2 starchy foods. Low-CN individuals displayed >6-fold higher breath methane levels in the fasting state and after starch ingestion than high-CN individuals (P = 0.001), whereas hydrogen excretion was similar.

Conclusions

Starchy foods are digested faster and produce higher postprandial glycemia in individuals with high AMY1 CN. In contrast, having low CN is associated with colonic methane production. This trial was registered at www.anzctr.org.au as ACTRN12617000670370.

Human amylase gene copy number variation as a determinant of metabolic state

INTRODUCTION

Humans have multiple genes encoding amylase that are broadly divided into salivary (AMY1) and pancreatic (AMY2) genes. They exhibit some of the greatest copy numbers of any human gene, an expansion possibly driven by increased dietary starch intake. Within the population, amylase gene copy number is highly variable and there is evidence of an inverse association between AMY1 copy number and BMI.

AREAS COVERED

We examine the evidence for the link between AMY1 and BMI, its potential mechanisms, and the metabolic effects of salivary and pancreatic amylase, both in the gastrointestinal tract and the blood

EXPERT COMMENTARY

Salivary amylase may influence postprandial 'cephalic phase' insulin release, which improves glucose tolerance, while serum amylase may have insulin-sensitizing properties. This could explain the favorable metabolic status associated with higher AMY1 copy number. The association with BMI is harder to explain and is potentially mediated by increased flux of undigested starch into the ileum, with resultant effects on short-chain fatty acids (SCFAs), changes in gut microbiota and effects on appetite and energy expenditure in those with low copy number. Future research on the role of amylase as a determinant of metabolic health and BMI may lead to novel therapies to target obesity.

Ketonuria may be associated with low serum amylase independent of body weight and glucose metabolism

CONTEXT

Ketonuria, which reflects a preferential combustion of lipids relative to carbohydrates, is often observed in lean rather than obese people. Clinical studies have shown that individuals with diabetes and/or obesity predispose to have low serum amylase (LSA).

OBJECTIVE

To investigate the association between ketonuria and LSA.

METHODS

We examined ketonuria assessed by dipstick urinalysis and clinical parameters including serum amylase in 3638 Japanese people aged 25-79 years who underwent a health-screening checkup.

RESULTS

There was an inverse relationship between body mass index (BMI) and serum amylase. The lowest serum amylase was observed in obese subjects (BMI ≥ 25.0 kg/m2) with positive ketonuria. Logistic regression analysis showed that ketonuria was significantly associated with LSA (<50 IU/L), which was not altered by the adjustments for relevant confounders including age, sex, BMI, and HbA1c.

CONCLUSIONS

Current results suggest a relative unavailability of carbohydrates for energy production in individuals with LSA.

Starch Digestion-Related Amylase Genetic Variant Affects 2-Year Changes in Adiposity in Response to Weight-Loss Diets: The POUNDS Lost Trial

Salivary and pancreatic amylases (encoded by AMY1 and AMY2 genes, respectively) are responsible for digesting starchy foods. AMY1 and AMY2 show copy number variations that affect differences in amylase amount and activity, and AMY1 copies have been associated with adiposity. We investigated whether genetic variants determining amylase gene copies are associated with 2-year changes in adiposity among 692 overweight and obese individuals who were randomly assigned to diets varying in macronutrient content. We found that changes in body weight (BW) and waist circumference (WC) were significantly different according to the AMY1-AMY2 rs11185098 genotype. Individuals carrying the A allele (indicating higher amylase amount and activity) showed a greater reduction in BW and WC at 6, 12, 18, and 24 months than those without the A allele (P < 0.05 for all). The association was stronger for long-term changes compared with short-term changes of these outcomes. The genetic effects on these outcomes did not significantly differ across diet groups. In conclusion, the genetic variant determining starch metabolism influences the response to weight-loss dietary intervention. Overweight and obese individuals carrying the AMY1-AMY2 rs11185098 genotype associated with higher amylase activity may have greater loss of adiposity during low-calorie diet interventions.

Relationship between salivary/pancreatic amylase and body mass index: a systems biology approach

BACKGROUND

Salivary (AMY1) and pancreatic (AMY2) amylases hydrolyze starch. Copy number of AMY1A (encoding AMY1) was reported to be higher in populations with a high-starch diet and reduced in obese people. These results based on quantitative PCR have been challenged recently. We aimed to re-assess the relationship between amylase and adiposity using a systems biology approach.

METHODS

We assessed the association between plasma enzymatic activity of AMY1 or AMY2, and several metabolic traits in almost 4000 French individuals from D.E.S.I.R. longitudinal study. The effect of the number of copies of AMY1A (encoding AMY1) or AMY2A (encoding AMY2) measured through droplet digital PCR was then analyzed on the same parameters in the same study. A Mendelian randomization analysis was also performed. We subsequently assessed the association between AMY1A copy number and obesity risk in two case-control studies (5000 samples in total). Finally, we assessed the association between body mass index (BMI)-related plasma metabolites and AMY1 or AMY2 activity.

RESULTS

We evidenced strong associations between AMY1 or AMY2 activity and lower BMI. However, we found a modest contribution of AMY1A copy number to lower BMI. Mendelian randomization identified a causal negative effect of BMI on AMY1 and AMY2 activities. Yet, we also found a significant negative contribution of AMY1 activity at baseline to the change in BMI during the 9-year follow-up, and a significant contribution of AMY1A copy number to lower obesity risk in children, suggesting a bidirectional relationship between AMY1 activity and adiposity. Metabonomics identified a BMI-independent association between AMY1 activity and lactate, a product of complex carbohydrate fermentation.

CONCLUSIONS

These findings provide new insights into the involvement of amylase in adiposity and starch metabolism.

Low AMY1 Gene Copy Number Is Associated with Increased Body Mass Index in Prepubertal Boys

Background

Genome-wide association studies have identified more than 60 single nucleotide polymorphisms associated with Body Mass Index (BMI). Additional genetic variants, such as copy number variations (CNV), have also been investigated in relation to BMI. Recently, the highly polymorphic CNV in the salivary amylase (AMY1) gene, encoding an enzyme implicated in the first step of starch digestion, has been associated with obesity in adults and children. We assessed the potential association between AMY1 copy number and a wide range of BMI in a population of Italian school-children.

Methods

744 children (354 boys, 390 girls, mean age (±SD): 8.4±1.4years) underwent anthropometric assessments (height, weight) and collection of saliva samples for DNA extraction. AMY1 copies were evaluated by quantitative PCR.

Results

A significant increase of BMI z-score by decreasing AMY1 copy number was observed in boys (β: -0.117, p = 0.033), but not in girls. Similarly, waist circumference (β: -0.155, p = 0.003, adjusted for age) was negatively influenced by AMY1 copy number in boys. Boys with 8 or more AMY1 copy numbers presented a significant lower BMI z-score (p = 0.04) and waist circumference (p = 0.01) when compared to boys with less than 8 copy numbers.

Conclusions

In this pediatric-only, population-based study, a lower AMY1 copy number emerged to be associated with increased BMI in boys. These data confirm previous findings from adult studies and support a potential role of a higher copy number of the salivary AMY1 gene in protecting from excess weight gain.

Low serum amylase and obesity, diabetes and metabolic syndrome: A novel interpretation

For the last decade, low serum amylase (hypoamylasemia) has been reported in certain common cardiometabolic conditions such as obesity, diabetes (regardless of type), and metabolic syndrome, all of which appear to have a common etiology of insufficient insulin action due to insulin resistance and/or diminished insulin secretion. Some clinical studies have shown that salivary amylase may be preferentially decreased in obese individuals, whereas others have revealed that pancreatic amylase may be preferentially decreased in diabetic subjects with insulin dependence. Despite this accumulated evidence, the clinical relevance of serum, salivary, and pancreatic amylase and the underlying mechanisms have not been fully elucidated. In recent years, copy number variations (CNVs) in the salivary amylase gene (AMY1), which range more broadly than the pancreatic amylase gene (AMY2A and AMY2B), have been shown to be well correlated with salivary and serum amylase levels. In addition, low CNV of AMY1, indicating low salivary amylase, was associated with insulin resistance, obesity, low taste perception/satiety, and postprandial hyperglycemia through impaired insulin secretion at early cephalic phase. In most populations, insulin-dependent diabetes is less prevalent (minor contribution) compared with insulin-independent diabetes, and obesity is highly prevalent compared with low body weight. Therefore, obesity as a condition that elicits cardiometabolic diseases relating to insulin resistance (major contribution) may be a common determinant for low serum amylase in a general population. In this review, the novel interpretation of low serum, salivary, and pancreas amylase is discussed in terms of major contributions of obesity, diabetes, and metabolic syndrome.